Conventional valves of this type, using a valve body which can be lowered or raised by a spindle in order to block or unblock a flow path between the inlet and outlet ports, tend to become leaky upon prolonged use on account of excessive wear of coacting surfaces and/or the accumulation of sediments along the edge of the valve seat. This generally requires the replacement of rubber gaskets or other parts of the assembly if not of the entire valve itself. In some instances, in which the valve housing is integrated in a larger structure, such replacement may be difficult or impossible.